390 SPHENOPHYLLUM. [CH. 



as a species of the genus Rotularia. The name Sphenophyllites 

 was proposed by Brongniart^ in 1822 as a substitute for 

 Schlotheim's genus, and in a later work^ the French author 

 instituted the genus Sphenophyllum. Dawson^ was the first to 

 make any reference to the anatomy of this genus ; but it is from 

 the examination of the much more perfect material from 

 St. Etienne, Autun, and other continental localities, the North 

 of England and Pettycur in Scotland, by Renault, Williamson, 

 Zeiller and Scott, that our more complete knowledge has been 

 acquired. 



The affinity of Sphenophyllum has always been a matter of 

 speculation; it has been compared with Dicotyledons, Palms, 

 Conifers (Ginkgo and Phyllodadus), and various Pteridophytes, 

 such as Ophioglossum, Tmesipteris, Marsilia, Salvima, Equisetum 

 and the Lycopodiaceae^ 



We may define the genus Sphenophyllum as follows : — 



Stem comparatively slender (1"5 — 15 mm.?), articulated, 

 usually somewhat tumid at the nodes ; the surface of the 

 internodes is marked by more or less distinct ribs and grooves 

 which do not alternate at the nodes, but follow a straight course 

 from one internode to the next. A single branch is occasionally 

 given off from a node. Adventitious roots are very rarely seen, 

 their surface does not show the ridges and grooves of the foliage- 

 shoots. 



The leaves are borne in verticils at the nodes, those in the 

 same whorl being usually of the same size, but in some forms 

 two of the leaves are distinctly smaller than the others. Each 

 verticil contains normally 6, 9, 12, 18 or more leaves, which are 

 separate to the base and not fused into a sheath ; the number 

 of leaves in a verticil is not always a multiple of six. They vary 

 in form from cuneiform with a narrow tapered base, and a lamina 

 traversed by several forked veins, to narrow uninerved leaves 

 and leaves with a lamina dissected into dichotomously branched 



1 Brongniart (22), PI. xiii. fig. 8, p. 234. 



2 lUd. (28), p. 68. 



3 Dawson (66), p. 153, PI. xii. 



^ For reference vide an excellent monograph by Coemans and Kickx (64), 

 also Potonie (94). 



